Method of attaching rubber to metal and articles produced thereby



P 2 3 J.'IG..\MALONE- I 2,078,917

METHOD OF ATTACXflNG RUBBER TO METAL ARTICLES PRODUCED THEREBY FiledAug. 24, v19:54

ATI'ORNEY Patented Apr. 27, 1937- UNITED STATES" mm QFFICE METHODons'rmcnmc nnnnan T METAL gun ARTICLES rnonncm THE John Gilbert Malone,Detroit, Mich. assignor, by

mesne assignments, -to-United States Rubber Company, New York, N. 12., acorporation of New Jersey- Application August 24, 1934, Serial No.141,200 '1 (or. 18-59) proper adhesion of the rubber to such a plating,it

is necessary for the copper and zinc to'be deposited in definiteproportions, about a 75% .cop-' per and 25% mm combination producingoptimum results. The proportions of copper and zinc, however, can onlybe controlled in an electro plating operation when the metal surface tobe treated is comparatively uniform in plane and is located in the bathata definite relative position to the anode. Where the article to berubber quality for a 75% coppergand 25% zinc com- 35 'ing an 'theelevated portions and on the edges than in coated is uneven andirregular in shape, the composition of the copper and in adeposit on thebase is not maintained uniform, nor for that matter, is the thickness ofthe deposit. In platuneven surface more metal deposits on thedepressions. This variation of thickness caused by directional effectmay be as much as 1 to for diflerent parts of the surface. Also, agreater percentage of copper is deposited in the depressions or hollowportions andva higher percentage of zinc is deposited alongtheprojections or edges of the article. Thimportance of obtaining auniformly proportionate deposit of the c pperand zinc is exemplifiedwhen it is considered that on the basis of 100% adhesion bination, a"100% copper plating produces an ad-v hesion quality of about 50%, andwhere the copper content drops to about 60% with about 40% zinc content,the adhesion quality of the rubber to the copper-zinc plating is vpractically nil. It has long since been suggested that rubber be adheredto metal by first dip-coating the metal with copper from a coppersulphate solution, but

as seen in the figures above, such a coating on I the base metalprovides an adhesion quality only half that obtainable with a 75% copperand mnc coating. According to the present invention, high qualityadhesion of'rubber to metal may be obtained by means of an alloy surfacewhich may be deposited by a so-called dip-coating: methodn' Bydip-coating" a metal base is meant the treatment of. thebase with asolution of the metals desired to be plated by a dipping, spraying,

spreading or other operation and allowing the plating operation toproceed merely by contact of the liquid with the base without the aid ofan external electric current as in an electro plating operatio'nq Themetal surface to which the rubber may be adhered according to thepresent invention is a bronze surface, that is, an alloy 5 comprising amajor proportion of copper and a minor proportion of tin, with orwithout small amounts of other metals, as is well known in her is to besecured, is provided. with a bronze surface preferably by a dip-coatingmethod, al-N though an electro plating method or a melting of the alloydirectly on the surface of the base 25 1 i may be employed.

The following example of coating 0. steel base. with rubber by firstdip-coating" the base with bronze is included merely. as an illustrationof the present invention and is not to be consldered as limiting thesame. The steel base was one designated in the trade as a 10-10 carbonsteel, hot rolled. vIt contains about .02% sulphur,

1 .00'7% phosphorus, 437% manganese, and .06%

carbon. The micro structure is considered ferrite with minute pearliteareas with no evidence of deformation due to cold working. This ismerely illustrative of the type of material which in large quantities iscoated with a rubber composition in commercial practice: Theconstituents of the 40 plating solution were Sn, which may be added assuch; Cu, which maybe added as CuSCn; and oxalate, which may be added as-potassium, 'sodium or ammonium oxalate, or as oxalic acid which ispreferably almost completely neutralized by hydroxide. An example of asatisfactory solutioncontains 2 to 3 ounces of oxalate per gallonprepared by neutralizing all but about .5 oz. per gallon of the oxalicacid with potassium, sodium, or ammonium hydroxide to a phenolphthaleinendpoint; .05'to .15 oz. pergallon oi'Bn as SnChZHzO: .002 paper gallonofcopper as disodium (or ammonium) dlaquo dioxalate cupriate prepared byadding copper sulphate toa hot solution ofsodlum oxalate, as forexample,

by adding a saturated copper sulphate solution to a solution containingabout 5 oz. of sodium oxalate per gallon until turbidity appears. Thedisodium (or ammonium) diaquc dioxalate may be prepared as described byFink and Wong Trans. Electrochem. 800., Vol. 63, pages 67-68, (1933) Thecoating solution should at all times be kept acid and it is preferableto apply the solution at a temperature between 50 and 60 C. A nveminute-treatment with the solution at such temperature issatisfactorybut a longer treatment is not detrimental. The surfacemay becoated by dipping into the solution or by spraying the solution on tothe surface, using'a compressed air operated spray jet. The metal andthe spray gun, however, should be free from oil andgrease or a uniformplating cannot be attained. A so-called rubber adhesion stock containinga vulcanizing agent was brought into contact with the driedbronze-coated steel base and vulcanized to the bronze coating by aheating operation as in present practice. An ad:-

hesion stock which is satisfactory .ona bronzed surface is set forthbelow, but many other different adhesion stocks may be used and theseare well known in the art of adhering rubber to metal surfaces:

' The above composition may be vulcanized to the metal by heating forone-half hour at 148 C.

A bronze coating plated on a metal by a dipcoating method, unlike brasscoated on a metal by an electroplating method, is of uniform thicknesseven over irregular portions of the article, and is of uniformcomposition at the same depth of the coating throughout the article.However, a dip-coating of bronze unlike the usual :clectroplatedcoatings gives a great variation in composition in the various layers ofthe coating itself, and a bulk analysis of the coatings is not a fairguide in determining the analysis of the coating for the best adhesionto a particular stock. The bulk analysis of, satisfactory coatings showsgenerally about 20% tin and over, but

the color of the. outer layers of the plating is a 55 much better guidethan bulk analysis and should be gold when deposited from anoxalate-coppertin solution. The proportion of copper to tin increases asthe deposition continues and is materially greater on the outer surfaceof'the coatings than adjacent the base. Analysis of the best coatingsfor adhesion show as a rule less than 15% tin in the outer coatinglayers, but with some stocks satisfactory adhesion may be obtained on asurface having as high a tin content as 30%, which is considerably morethan the usualrun'of commercial bronzes. It is considered that thisvariation in the proportion of the diifereht ingredients of the alloybetween the outer surface of the coating and' the surface ad- Jacent thebase may be a cpnsiderable factorin .the production of successfulcoatings by the present invention. 7

The example above shows a dip-coating of bronze on ferrous metal foradhesion of rubber to ferrous metal, but the bronze may be coated onany-metal to which a is desired :8 aidhere -the rubber-"stock. As abovestated, the

bronze may, if ,desired, be coated on the metal 7 stock bymelting-thesame on to a clean surface of the stock, or, by-an electroplating, aswell as by a dip-coating'process, as above described. If

it is desired to. adhere a rubber composition to a bronze base and thebase isof a proper composition forsecuring the desired rubber combronzeis too high in tin, it maybe dip-coated with an axalato-copper-tinsolution as above'described. If, however, the bronze is of too high acopper content, or if, for example, it is desired to secure rubber,directly to a copper surface, then it is necessary to first plate thehigh-copper bronze or the copper base with a metal, such as tinfto'whlchboth the base and the desired dipcoated bronze surface will adhere. Forexample, in dip-coating a copper surface, the cleaned copper surface maybe coated with SnCh and water in the form of a paste which is thenrubbed well with a wire brush to producea tinned'surface to which afterwashing the bronze may be applied by the dip-coating method as above.The samemethod is applicable in the case of a highcopper bronze where itis desired to ,plate a bronze coating of lower copper content for thedesiredadhesion.

By dip-coating the base with ari acid aqueous oxalate solutioncontaining copper and tin, coatings having less tendency to stainspotting" than coatings from alkaline cyanide solutions as in brasselectro-plating are obtained. since it is known that alkaline compoundsare more likely to cause this spotting out than acid substances. Thisspotting out is believed to'deleteriously affect the adhesion of therubber, and experiments have shown that a small amount of residualoxalic acid on the metal coating does not impair adhesion of the rubbercomposition while smallamounts of residual cyanide do.

at various temperatures and for different periods of time depending onthe composition of the same as is well-known in the art. Variousmodincations of the invention will occur to those skilled in the art andit is not intended to limit the invention other than as set forth in theappended claims.

Having thus described my invention, what I claim and desire to protectby Letters Patent is: 1. A new article of manufacture comprising a rrousbase, a bronze coating comprising a major proportion of copper and aminor proportion of tin on said base, the proportion of copper to tin insaid bronze being materially greater on the I outer surface of saidcoatingJghan adjacent the said base, the tin content of said outersurface being up to 15; percent and arubber'layer vulcanized on saidcoating.

2. A new article of manufacture a metallic base, a bronze coatingcomprising a major proportion of copper and a minor proportion of tin onsaid base, the proportion of copper to tin in said bronze beingmaterially greater on the outer surface of said coating than adjacentthe said base, analysis of the outer surface of the analysis of theentire thickness of coating showing at least 20% tin, and a rubber layervulcanized on said coating.

5 3. A new article of manufacture comprising aferrous base, a bronzecoating comprising a major v proportion of copper and a minor proportionof tin on said base, the proportion of copper to tin in said bronzebeing materially greater onthe' in outer surface of said coating thanadjacent the said base.. analysis .ofthe outer surface of the coatingshowing at the most 15% tin and bulk 1 analysis of the entire thicknessof coating showing at least 20% tin, and a rubber layer vulcanized 15 onsaid coating. 1 e

'4. The methodof attaching-rubber to metal which comprises dip-coating abronze containing up to15 percent tin in the outer layers upon the metalfrom a solution containing copper and tin, 2 0 bringing rubbercontaining a vulcanizing agent into engagement with the coated surface,and

vulcaiilizing the rubber onto said Surface.

5.: The-method of-attaching' rubber to ferrous metal which comprisesdip-coating a bronze con- 25taining u'p'to 15 percent tin in the outerlayers ame'pr: j I 3 coating showing at the most 15% tin and bulk;

upon the ferrous metal from an aqueous solution containing'copper andtin, bri ein rubber cona vulcanizing agent into engagement with 1 thecoated surface, and vuleanizing the rubber onto said surface.

6. The method of attaching rubber to metal which comprises dip-coating abronze containing up to 15 percent tin in the outer layers andwith abulk analysis of the entire thickness of the coating showing at least 20percent tin upon the metal 10 from an aqueous solution containing copperand 'tin, bringing rubber'containing a vulcanizing .coated surface, andvulcanizing the rubber onto said surface. r

. JOHN GILBERT MALONE 25

